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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Velocity inconsistent
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<blockquote data-quote="Fiftydriver" data-source="post: 678984" data-attributes="member: 10"><p>I do get a kick out of guys bragging about their rifles that get single digit extreme spreads. Thats great if they are actually doing it and there are some guys on here that are reporting such results that I believe 100% because I know them personally but on average, this is not attainable or even needed.</p><p> </p><p>Generally speaking the lowest extreme spreads will come from larger caliber chamberings, 338s and 375s are famous for low ES velocity numbers. As the bore size gets smaller, especially if case capacity stays the same, ES usually will increase on average. For example, its pretty easy to get a 338 Edge to produce ES well under 20 fps and often into the low teens and even single digits for a given 10 shot string.</p><p> </p><p>A 300 RUM will generally easily get into the sub 30 fps ES range, often times into the 20 fps range but its rare to see a 300 RUM get much tighter then that.</p><p> </p><p>A 7mm RUM will generally break well under 50 fps ES and often times into sub 40 fps spreads but its rare to see one get much under 30 fps for a 10 shot string.</p><p> </p><p>Why is this...... Well, my theory is that the slower burning powders simply are not as good at producing very consistant velocities as the quicker burning powders are. That is not to say they are inconsistant, just not quite as consistant as the bigger bores. Also, I believe that in the smaller bores, minute variations in temp, Bar pressure, bore temp, bullet jacket thickness, bullet weight, baring surface length and several other areas will make a larger effect on final muzzle velocity on the smaller bullets then on the larger caliber bullets.</p><p> </p><p>An example, if you have a group of 175 gr 7mm bullets that vary by 2 grains over 20 bullets, thats a 1,14% varitation in weight.</p><p> </p><p>If you take another 20 bullets in say a 300 gr 338 version that have the same 2 grain variation, thats a 0.66 % variation. </p><p> </p><p>Now its not uncommon to see weight variation in bullets, Baring surface lengths can vary greatly as well and that makes a much great difference in the smaller caliber chamberings.</p><p> </p><p>Simply put, if you get a load that will produce good consistant, ROUND shaped groups at 100 yards and has an ES of less then 50 fps. Test that load at long range before you start chasing that magical ULTALOW Extreme Spread. A 50 fps extreme spread will make much more difference on paper or on your ballistic program then it will in reality when actually putting bullets in the air. Much over 50 fps and yes I would say try something else.</p><p> </p><p>If your under 50 fps acceptable if the load is consistant in the accuracy department. Under 40 fps is good, under 30 fps is great, under 20 fps extremely good and anything under that, well, going to ruffle some feathers here but YOUR LUCKY!!!</p><p> </p><p>I do not get to hung up on velocity spreads. In fact I seldom shoot a 10 shot string to get a meaningful ES. Shooting at long range will instantly tell you if your velocity spreads are to high as you will see noticabl vertical variation in your shot impacts.</p><p> </p><p>Have seen many rifle/load combos that would produce easy sub 3/4 moa groups at 1/2 mile that had extreme spreads of between 30 and 50 fps. I even own a 22-250 AI that will put the 55 gr Ballistic tip into sub 2" groups at 500 yards even though it has a legit 90 to 100 fps ES for 10 shot strings....... GO figure....</p><p> </p><p>Don't get to hung up on extreme spreads, thats a good way to waste more of the accuracy life of your barrel!!! Test at long range, use a chrono to get a base idea of your muzzle velocity and then start testing your drop charts at long range. In the end, you will need to correct for your MV and many other factors to get your drop chart to match up perfectly with your actual trajectory so in the end, it means very little to putting your bullet on the mark that first shot.</p></blockquote><p></p>
[QUOTE="Fiftydriver, post: 678984, member: 10"] I do get a kick out of guys bragging about their rifles that get single digit extreme spreads. Thats great if they are actually doing it and there are some guys on here that are reporting such results that I believe 100% because I know them personally but on average, this is not attainable or even needed. Generally speaking the lowest extreme spreads will come from larger caliber chamberings, 338s and 375s are famous for low ES velocity numbers. As the bore size gets smaller, especially if case capacity stays the same, ES usually will increase on average. For example, its pretty easy to get a 338 Edge to produce ES well under 20 fps and often into the low teens and even single digits for a given 10 shot string. A 300 RUM will generally easily get into the sub 30 fps ES range, often times into the 20 fps range but its rare to see a 300 RUM get much tighter then that. A 7mm RUM will generally break well under 50 fps ES and often times into sub 40 fps spreads but its rare to see one get much under 30 fps for a 10 shot string. Why is this...... Well, my theory is that the slower burning powders simply are not as good at producing very consistant velocities as the quicker burning powders are. That is not to say they are inconsistant, just not quite as consistant as the bigger bores. Also, I believe that in the smaller bores, minute variations in temp, Bar pressure, bore temp, bullet jacket thickness, bullet weight, baring surface length and several other areas will make a larger effect on final muzzle velocity on the smaller bullets then on the larger caliber bullets. An example, if you have a group of 175 gr 7mm bullets that vary by 2 grains over 20 bullets, thats a 1,14% varitation in weight. If you take another 20 bullets in say a 300 gr 338 version that have the same 2 grain variation, thats a 0.66 % variation. Now its not uncommon to see weight variation in bullets, Baring surface lengths can vary greatly as well and that makes a much great difference in the smaller caliber chamberings. Simply put, if you get a load that will produce good consistant, ROUND shaped groups at 100 yards and has an ES of less then 50 fps. Test that load at long range before you start chasing that magical ULTALOW Extreme Spread. A 50 fps extreme spread will make much more difference on paper or on your ballistic program then it will in reality when actually putting bullets in the air. Much over 50 fps and yes I would say try something else. If your under 50 fps acceptable if the load is consistant in the accuracy department. Under 40 fps is good, under 30 fps is great, under 20 fps extremely good and anything under that, well, going to ruffle some feathers here but YOUR LUCKY!!! I do not get to hung up on velocity spreads. In fact I seldom shoot a 10 shot string to get a meaningful ES. Shooting at long range will instantly tell you if your velocity spreads are to high as you will see noticabl vertical variation in your shot impacts. Have seen many rifle/load combos that would produce easy sub 3/4 moa groups at 1/2 mile that had extreme spreads of between 30 and 50 fps. I even own a 22-250 AI that will put the 55 gr Ballistic tip into sub 2" groups at 500 yards even though it has a legit 90 to 100 fps ES for 10 shot strings....... GO figure.... Don't get to hung up on extreme spreads, thats a good way to waste more of the accuracy life of your barrel!!! Test at long range, use a chrono to get a base idea of your muzzle velocity and then start testing your drop charts at long range. In the end, you will need to correct for your MV and many other factors to get your drop chart to match up perfectly with your actual trajectory so in the end, it means very little to putting your bullet on the mark that first shot. [/QUOTE]
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